Characteristics optimizing of LDMOS devices with Advanced-RESURF

Nowadays, different types of high-voltage devices which are usually utilized in MOS technology are presented; such as LDMOS, VMOS, DSMOS and etc. LDMOS is more practically useful rather than others especially in radio frequency amplifiers. First, fundamental principles of LDMOS design and important effects of DC such as quasi-saturation, self-heating and impact-ionization were entirely investigated. But the most significant problem in HV-MOS devices which has maintained from past is tradeoff between breakdown-voltage, on-resistance, Current intensity and frequency. As it was later mentioned, the designation of LDMOS with structure of Reduced Surface Field (RESURF) of this device caused increasing in breakdown-voltage and decreasing in on-resistance in the best way. We tried to improve the characteristics of LDMOS with presenting methods. In fact, four steps of a RESURF which bring about improving the specifications of LDMOS were studied. They respectively are Single-RESURF, Double-RESURF, Dual-conduction-RESURF and Advanced-RESURF. One of the most complete types of LDMOS which is Advanced-RESURF were investigated and made by using addition of n-top to p-buried (Fig 1). In this device, in comparison with Single-RESURF, there was an increase about 1.5 times in current intensity, 1.4 times in frequency and 1.2 times in breakdown-voltage (Fig 2). Furthermore, mounting in pollution n-top effect brought about rising in frequency and breakdown-voltage while the current intensity remained stable. it was observed that with moving n-top and p-buried from gate to drain, frequency and breakdown-voltage were substantially increased. On the other hand, when the two mentioned layers became closer towards the drain, increasing in breakdown-voltage diminished(Fig 3).